1. Field of the Invention
The present invention relates to a polyester composition, especially polybutyleneterephthalate (hereinafter designated PBT) composition which can be molded in the usual way to form a shaped article having excellent physical properties and excellent flame resistance with reduced tendency to drip during combustion.
In essence the composition comprises (a) a polyester the main component of which is polybutyleneterephthalate, (b) a halogenated diphenylether, optionally decabromodiphenyl as a flame retarding agent, and (c) diepoxy compounds.
2. Description of the Prior Art
In recent years, PBT resins have been investigated and developed as molding materials because of their excellent moldability and their possession of a good balance of physical properties. Such resins have been expected to be widely used as excellent engineering plastics and raw materials for machine parts, electrical equipment, motor cars, and housings.
The engineering plastics are strictly required to have excellent flame resistance in addition to a good balance of chemical and physical properties.
Accordingly, it is of considerable commercial importance to be able to impart excellent flame resistance to PBT resins without any substantial impairment of their physical properties.
In order to provide a flame retardant PBT composition various additives have heretofore been proposed. However, these compositions have been quite unsatisfactory in many commercial uses.
As an example, reference may be made to Japanese patent publication (Tokkaisho No. 46-2086). According to this prior publication, an improved PBT composition has been proposed wherein decabromodiphenyl is added in combination with antimony trioxide.
Though the shaped article obtained from this composition has rather satisfactory flame resistance, it has a poor surface appearance with many brown or black spots, and it exhibits deteriorated physical properties, particularly low tensile elongation at the break point. Therefore, this composition cannot be used successfully in commercial practice.
As another example, reference may be made to U.S. Pat. No. 3,624,024, which proposes an improved PBT composition comprising brominated diphenyl or brominated diphenylether as flame retardants, together with talc. Although the shaped article obtained from this PBT composition has satisfactory flame resistance and has a high heat distortion temperature, it has poor tensile elongation at break, which is considered to be undesirable for many commercial uses.
An object of this invention is to provide an improved PBT composition which can produce a shaped article having excellent flame resistance with reduced tendency to drip during combustion, and which has good appearance and high tensile elongation at break.
It has been discovered according to the present invention that excellent results can be attained by forming a PBT composition containing a halogenated diphenylether in combination with a small amount of a diepoxy compound.
A composition comprising polyethyleneterephthalate and diepoxy compounds has already been described in Japanese patent publication No. 46-10671. It is stated in this reference that polyethyleneterephthalate shaped articles made from this composition have high impact strength and good dimensional stability. However, this reference does not teach the combination of flame retarding additives with diepoxy compounds.
Moreover, this reference does not teach or suggest that a PBT shaped article acquires superior flame resistance an excellent balance of physical properties, especially high tensile elongation at break, and good appearance by reason of the combination of specific flame retarding additives with certain diepoxy compounds.